A study of the kinetics and mechanism of the decay of R-acetoxy-N-nitrosopyrrolidine and R-acetoxy-N-nitrosopiperidine are reported. The compounds differ in reactivity by more than 2 orders of magnitude at physiological pH. On the basis of thermodynamic parameters, common ion inhibition and azide ion trapping experiments, both compounds appear to decompose under these conditions by the formation of N-nitrosiminium ion intermediates. The differences in reactivity are rationalized on the basis of results from an ab initio study, described in the accompanying paper. The first direct study of the kinetics of decay of cyclic R-hydroxynitrosamines of nitrosopiperidine and nitrosopyrrolidine and a third compound, 2-hydroxy-2-methylnitrosopyrrolidine is also summarized. These prove to be highly unstable reactive intermediates, in contrast to what might be expected on the basis of earlier reports concerning cyclic R-hydroxynitrosamines.

The decay of α-(acyloxy)dialkylnitrosamines in aqueous solutions has been studied with a view toward elucidating mechanistic details and effects of structure on mechanism and reactivity. Rate constants (k 1) for the pH-independent decay of 43 α-(acyloxy)dialkylnitrosamines have been determined. Observations from these and other experiments rule out decomposition via an anchimeric assistance mechanism involving the Z isomer that had previously been suggested. All of the reported data for most of the compounds is consistent with a mechanism involving the formation of N-nitrosiminium ions in or before the rate-limiting step. Structure−reactivity correlations indicate that the stability of α-(acyloxy)dialkylnitrosamines is determined by electronic properties of substituents at RN and RC as well as by the ability of substituents RC to engage in hyperconjugative interactions of C−H bonds with the developing cationic center in the transition state for nitrosiminium ion formation. Attachment of substituents of sufficient electron-withdrawing power at RN and RC results in a predicted change in mechanism to what appears to be an acyl group attack mechanism.

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